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Problems of etiology, taxonomy and nomenclature offiloviruses, epidemiology, morbidity with a little-known by Russian medics especially dangerous exotic infectious disease - Ebola fever are examined. Significant distinguishing features of 2013 - 2015 epidemic in West Africa were de- tected - along with its unprecedented length, a decline did not take place as in previous outbreaks, neither causative agent virulence, nor infectivity of the infection during multiple generations from human to human. Literature data analysis allowed to assume that in the process of epidemic focus formation Ebola virus changes its properties and cyclically passes through several successive in- terconnected phases: an initial reservation phase in unknown ecosystems - animals, either plant, soil or water; intermediate phase of epidemic spread with primary acquisition of high virulence for humans, and then its decline; final stage of hidden circulation of causative agent that is ap- athogenic for humans. This hypothetical chain of natural phases' transitions of Ebola virus allows to explain and link together phenomenology of this causative agent - rapid fall of virulence and infectivity for humans in foci in dynamics of epidemic outbreaks, quite a high population immunity in nosoareal of the causative agent in Africa, that contradicts the established understanding of its high lethality for humans.

In the last quarter of century virus of Rift valley fever (RVF) sharply extended its distribution by moving from Africa to Asia and evolving from low- to high pathogenic for humans causing severe hemorrhagic disease, practically equaling in this respect with some members ofa group of extremely dangerous pathogens. Morbidity and epidemics of RVF are analyzed. Evolution of epidemic development of the infection is examined. Necessity of development of means and methods for diagnostics, prophylaxis and therapy of RVF is underlined.

The evaluation of the biological and epidemiological properties of Ebola, Marburg, Lassa, and Machupo viruses suggests that they are of social importance for health care authorities. The studies have created prerequisites to the development of reliable biosafety means against these pathogens. Particular emphasis is laid on the methods for infection diagnosis and on the studies to design specific protective agents--immunoglobulins and inactivated vaccines.

In this review modern data on dangerous and particularly dangerous viral haemorrhagic fevers caused by a group of viruses belonging to the families of phylo-, arena-, flavi-, bunya- and togaviruses are presented. Morbidity rates and epidemics caused by Marburg virus, Ebola fever virus, Lassa fever virus, Argentinian and Bolivian haemorrhagic fever viruses, dengue haemorrhagic fever virus, Crimean haemorrhagic fever virus, Hantaviruses are analyzed. Mechanisms of the evolution of the epidemic manifestation of these infections are considered. The importance of the development of tools and methods of diagnosis, rapid prevention and treatment of exotic haemorrhagic fevers is emphasized.